The present invention relates to antennas and more particularly to a planar multiple band omni radiation pattern antenna having significant gains in the operating frequencies.
A conventional antenna such as coaxial sleeve antenna mounted in a wireless communication device is illustrated in FIG. 1. As shown, the antenna comprises a coaxial transmission line 10 including an inner conductor (or core) 14, an outer conductor (or shielded mesh or ground line) 16, and a cylindrical film 17 of insulated dielectric material sandwiched between the inner and outer conductors 14 and 16 so that a concentric conductor as known in the electromagnetism is formed by both the inner and outer conductors 14 and 16. Also, an insulated cylindrical shell 19 is formed around the coaxial transmission line 10. The shell 19 has one end coupled to a control circuit (not shown) of a wireless communication device. A metal sleeve 18 is formed around the other end of the shell 19. The sleeve 18 and the outer conductor 16 are coaxial. The sleeve 18 has the top end coupled to the outer conductor 16 and the other portion not in contact with the outer conductor 16 by means of the shell 19 therebetween. An extension 12 is projected from the inner conductor 14 at the other top end of the coaxial transmission line 10. The extension 12 is above the sleeve 18 by a distance (i.e., length of the extension 12) about the length of the sleeve 18. But the length of each of the extension 12 and the sleeve 18 is slightly less than one-quarter wavelength at an optimum operating frequency (i.e., xc2xc where 1 is wavelength of the operating frequency). As such, another concentric conductor is formed between the sleeve 18 and the outer conductor 16 for preventing the antenna from being interfered by a leakage current at the cylindrical surface of the outer conductor 16. Hence, a balum (i.e., balance-to-unbalance) converter is formed. As an end, a desired antenna radiation is generated by the coaxial sleeve antenna.
Typically, an omni radiation pattern antenna is mounted in a mobile or portable wireless communication device such as the widely used cellular phone. As a result, the wireless communication device can achieve a communication of 360 azimuthal degrees. The above sleeve antenna is the antenna being most widely mounted in the wireless communication device. Also, the sleeve antenna is widely mounted in a wireless communication device capable of receiving or transmitting signals at frequencies such as high frequency (HF), very high frequency (VHF), and ultra high frequency (UHF). The basic structure of the sleeve antenna is a metal sleeve. A balum converter is formed on the coaxial sleeve antenna. Moreover, a collinear structure is implemented in the coaxial sleeve antenna for increasing antenna gain and omni radiation pattern.
There has been a significant growth in wireless local Area network (WLAN) due to an increasing demand of mobile communication products in recent years in which IEEE 802.11 WLAN protocol is the most important one among a variety of WLAN standards. The IEEE 802.11 WLAN protocol was established in 1997. The IEEE 802.11 WLAN protocol not only provides many novel functions for WLAN based communication but also proposes a solution for communicating between mobile communication products made by different manufacturers. There is no doubt that the use of the IEEE 802.11 WLAN protocol is a milestone in the development of WLAN. The IEEE 802.11 WLAN protocol was further modified for being adapted to serve as a standard of both IEEE/ANSI and ISO/IEC in August 2000. The modifications comprise IEEE 802.11a WLAN protocol and IEEE 802.11b WLAN protocol. In an expanded standard physical layer, the operating frequencies have to be set at 5 GHz and 2.4 GHz. As such, the well-known coaxial sleeve antenna cannot satisfy the requirement of enabling a mobile communication product to use both IEEE 802.11a and IEEE 802.11b WLAN protocols at the same time. Instead, several antennas have to be mounted in the product for complying with the requirement of frequency band. However, such can increase a manufacturing cost, complicate an installation procedure, and consume precious space for mounting the antennas. As a result, the size of the product cannot be reduced, thereby contradicting the compactness trend.
Recently, there is a trend among wireless communication product designers and manufacturers to develop an antenna capable of operating in two different frequency bands (i.e., dual frequency) in developing communication products of dual frequency or multi-frequency. It is envisaged that the use of multi-frequency antenna in a wireless communication product can decrease the number of antennas provided therein and occupied space thereon. Unfortunately, commercially available multi-frequency antennas such as chip antennas or patch antennas made by a printing process are poor in performance at an operating frequency of 5 GHz. Some antennas such as one disclosed in U.S. Pat. No. 4,509,056 can meet required features. However, it is bulky or complicated in structure, resulting in an increase of manufacturing and assembly costs and unnecessary consumption of installation space. Further, a desired omni radiation is not easy to achieve if a radiation pattern has only one element. In addition, a high variation is occurred in manufacturing antennas operable in microwave due to very short wavelength of the microwave, resulting in a low yield. Hence, a need for improvement exists.
A primary object of the present invention is to provide a planar multiple band omni radiation pattern antenna. By utilizing this, the above drawbacks of the prior art such as bulky, complicated structure, uneasy to achieve the omni radiation, and low yield can be overcome.
One object of the present invention is to print first and second patch lines on a planar dielectric substrate material. A plurality of radiation members are formed bifurcately, symmetrically along both sides of a longitudinal axis of either patch line. Each of the radiation members comprises at least two post-shaped conductors each having a length slightly less than one-quarter wavelength of a central frequency of each operating frequency so as to form a choke and the radiation members of multi-frequency. Most importantly, the operating frequencies need not be harmonically related.
Another object of the present invention is to provide a planar printed antenna capable of operating at a plurality of frequencies of microwave. A radiation pattern of the antenna can cover 360 azimuthal degrees. Moreover, the radiation pattern of the antenna is printed on the dielectric substrate material. Thus, the present invention can decrease variations in the manufacturing process, increase yield and efficiency, and lower the manufacturing cost.
Still another object of the present invention is to provide an antenna having a collinear structure so as to compensate an antenna gain. As a result, the antenna not only can have an omni radiation pattern (i.e., azimuth) similar to that of the prior art sleeve antenna but also can have an antenna gain higher than that of the prior art sleeve antenna. Thus, the antenna is particularly suitable to microwave applications.
A further object of the present invention is to adjust a parasitic effect among the post-shaped conductors by suitably changing their shapes in order to obtain a resonance of multi-frequency.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.